Tele lens - forget it. 500mm f/8 is a bad start, even before you double it to 1000mm f/16. Both are in the diffraction softening zone of the 50D, and without IS you're going to find it hard to keep motion blur controlled.

The tele/wide angle converter is more interesting, within the limits of it's cheap enough possibly for a gamble. I wouldn't expect the tele adapter to give decent quality, but I have ordered a similar wide angle in the past on a much smaller mount. The optics were much better made than I thought. Glass made with anti-reflection coatings. Unfortunately in combination with an already wide angle lens, it hard vignetted badly. Might be ok on a longer focal length lens, but then that kinda defeats the point of getting it in the first place.

If you want a decent quality super tele-photo (500mm) try this.
It was relatively cheap (150EUR) used on eBay.
And the Tamron is one of the better ones! You just need to get the right Adaptall adapter...

With this lens I did this one:

and that one:
Large original available, just click through this image to "all sizes"

You could get some of those lenses off of eBay (not referring to the mirror lens), or mount a soda can with the top cut off and a little hole drilled into the bottom. I guess what I'm trying to say is that either way, none will give you the kind of quality you bought a DSLR for. Save up for a decent lens, ignore this junk...